(Meth)acrylic acid is generally prepared by gas-phase oxidation of a compound such as propane, propylene, (meth)acrolein, etc. in the presence of a catalyst. For example, propane, propylene, etc. is converted into (meth)acrylic acid through (meth)acrolein by gas-phase oxidation in the presence of an appropriate catalyst in a reactor, and a mixed gas of reaction products containing (meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, an inert gas, carbon dioxide, water vapor, and various organic by-products (acids, low boiling point by-products, high boiling point by-products, etc.) by the reaction is obtained in the back end of the reactor.
The mixed gas containing (meth)acrylic acid is generally obtained as (meth)acrylic acid by purification through a process illustrated in FIG. 1.
In detail, the mixed gas containing (meth)acrylic acid contacts an absorption solvent including water in a (meth)acrylic acid absorption tower 100, and is recovered as a (meth)acrylic acid aqueous solution. Further, (meth)acrylic acid-stripped insoluble gas is recycled for a synthesis reaction of (meth)acrylic acid, and a part thereof is incinerated, converted into harmless gas, and discharged. The (meth)acrylic acid aqueous solution is extracted through an extraction tower 200, or is directly to be fed to a water separation tower 300. Water separated from the (meth)acrylic acid aqueous solution is recovered from the upper part of the water separation tower 300, and a (meth)acrylic acid-containing mixture is recovered from the lower portion of the water separation tower 300. The (meth)acrylic acid-containing mixture recovered from the lower portion of the water separation tower 300 is distilled in a high-boiling-point material separation tower 400 to obtain a crude (meth)acrylic acid, which is finally purified in a crystallizer 500 to obtain (meth)acrylic acid.
In this regard, a waste liquid containing Michael adducts such as a dimer to a pentamer of (meth)acrylic acid is obtained from the high-boiling-point material separation tower 400. As a method to increase yield of (meth)acrylic acid, a method of additionally recovering (meth)acrylic acid by feeding the waste liquid to an acrylic acid recovery apparatus 600 and decomposing the Michael adducts in the waste liquid is known.
However, since maleic acid contained in the waste liquid is easily precipitated, it causes the blockage of pipes in the acrylic acid recovery apparatus 600 and raises the viscosity of the waste liquid to reduce the decomposition efficiency of the Michael adducts.
To solve these problems, a method of using a forced circulation type of heat exchanger was suggested. However, this method increases investment costs, because an expensive pump is used in the forced circulation type of heat exchanger. Further, in the method of using the forced circulation type of heat exchanger, high-temperature and high-viscosity waste liquid is used as it is, and therefore, it takes a long time to transfer the waste liquid, which may cause a problem with the pump, and there is also a fatal disadvantage that operation stability of the process is low.